The following pictures show how I setup my scope.
This shows the heaters and temperature sensor attached to the rear of my diagonal. One of the metal vanes was removed and replaced with a very thin section of double sided PCB. I masked out some tracks with insulation tape which was then etched to leave a few traces for connecting the heaters and sensor, two thick traces for the heaters power and two thinner ones for the sensor. The heaters themselves are mounted onto a small PCB I made. The temperature sensor is just glued to the back of the mirror.
The wires from the diagonal pass through a small hole and grommet in the side of the tube. The ambient temperature sensor is also mounted here, you can just see it sticking out from underneath the rubber insulation material. My scope is wrapped in this and then covered in a canvas material, it stops the tube from dewing up and getting all wet. It also helps protect the scope during transportation. Lastly I run all the various wires under it to keep it neat and tidy.
Picture of two heaters attached to my finder scope. You can see another view of how the scope was wrapped in the high density foam and canvas. The grey wire that is poking out from under the front heater band is the finders temperature sensor.
The last image shows the rear mirror cell with the fan attached. I have routed out a circular piece of hardboard that attaches directly to the original fan mounting holes. The fan is orientated so that it sucks air out of the tube, I found this to be the most efficient method. Just by sticking the fan on by itself one is not guaranteed where the air is being sucked or blown from, this way the air can only come from inside the tube. I also prefer the fan to suck, as it lessens the chance of dust and dirt being forced into the tube and onto the mirror. The main mirror temperature sensor can be seen entering the scope near the bottom half of the insert. The sensor is then taped to the rear of the mirror.